Heavy rain is expected to spread across the North Island from the north Tasman Sea and affected areas can expect heavy rain from midday through to Sunday morning, spokeswoman Sarah Garlick said.

MetService predicts 25 to 40mm per hour downfalls over Waitomo, Taumarunui, western Taupo and northern Taranaki late Saturday afternoon, evening and night, and for similar amounts to hit Waikato Saturday night and early Sunday morning.

There is still uncertainty regarding the timing and exact location of severe outbursts. However, there is a risk that rainfall amounts could be greater than 50mm within six hours, especially in north Taranaki, Waitomo and Taumarunui.

Localised downpours could also cause surface flooding from Waikato to North Taranaki.

Coromandel and eastern Bay of Plenty are more likely to see heavy rainfalls on Sunday.

People in these areas should be on the lookout for threatening weather and listen for possible weather warnings, Garlick said.

Heavy rain has eased about Westland and the weather watch for that area is now lifted.